1. Field of the Invention
This invention relates to the detection of the characteristics of an incident light distribution, particularly but not exclusively for use with display devices including a touch input.
2. Description of the Related Art
Various touch-screen technologies are well-known and widely used. They include so-called ‘resistive’ and ‘capacitive’ technologies. Most such technologies however add significant cost and complexity to a display module, and impair front-of-screen performance.
There is some interest in using photodiodes or other light sensors within the display matrix to detect light from the display scattered back by a finger placed on the screen surface and/or detect ambient-light shadows cast by fingers or a stylus held against the screen. Such approaches offer a low-cost and highly integrated route to providing basic ‘touch-screen’ functionality.
However, using light sensing in order to detect the presence and position of a user's finger is not accurate. In particular, the user's finger makes contact with the top surface of the display device, whereas the sensor circuitry is most preferably integrated into the active plate of the display. The spacing between the active plate and the surface of the display means that a point of contact cannot be derived unambiguously from a shadow cast. This problem is compounded if there is more than one directional light source.